Als Gregor Samsa eines Morgens aus unruhigen Träumen erwachte, fand er sich in seinem Bett zu einem ungeheueren Ungeziefer verwandelt.
Is "erwachte" in the imperfect tense here? And why is it at the end of the first clause? I thought verbs go at the end for dependent clauses but isn't the second clause the dependent one because it adds information to the first one?